CONTENTS. Xlll 



SECTION XXI. 



Polarization of Light Defined Polarization by Refraction Properties of the 

 Tourmaline Double Refraction All Doubly Refracted Light is Polarized 

 Properties of Iceland Spar Tourmaline absorbs one of the two Refracted 

 Rays Undulations of Natural Light Undulations of Polarized Light 

 The Optic Axes of Crystals M. Fresnel's Discoveries on the Rays passing 

 along the Optic Axis Polarization by Reflection .... Page 200 



SECTION XXII. 



Phenomena exhibited by the Passage of Polarized Light through Mica and 

 Sulphate of Lime The Coloured Images produced by Polarized Light pass- 

 ing through Crystals having one and two Optic Axes Circular Polarization 

 Elliptical Polarization Discoveries of MM. Biot, Fresnel, and Professor 

 Airy Coloured Images produced by the Interference of Polarized Rays 209 



SECTION XXIII. 



Objections to the Undulatory Theory, from a difference in the Action of 

 Sound and Light under the same circumstances, removed The Disper- 

 sion of Light according to the Undulatory Theory .... 220 



SECTION XXIV. 



Chemical or Photographic Rays of the Solar Spectrum Messrs. Scheele's, 

 Ritter's, and Wollaston's Discoveries Mr. Wedgewood's and Sir Humphry 

 Davy's Photographic Pictures The Calotype, the Daguerreotype, theChro- 

 matype, the Cyanotype Sir John HerschePs Discoveries in the Photo- 

 graphic or Chemical Spectrum Mons. E. Becquerel's Discovery of Inactive 

 Lines in the Chemical Spectrum 224 



SECTION XXV. 



Heat Calorific Rays of the Solar Spectrum Experiments of MM. De Laroche 

 and Melloni on the Transmission of Heat The Point of greatest Heat in 

 the Solar Spectrum varies with the Substance of the Prism Polarization of 

 Heat Circular Polarization of Heat Transmission of the Chemical Rays- 

 Absorption of Heat Radiation of Heat Dew Hoar Frost Rain Hail 

 Combustion Dilatation of Bodies by Heat Propagation of Heat Latent 

 Heat Heat presumed to consist of the Undulations of an elastic Medium 

 Parathermic Rays Moser's Discoveries 238 



SECTION XXVI. 



Atmosphere of the Planets and the Moon Constitution of the Sun Estima- 

 tion of the Sun's Light His influence on the different Planets Tempera- 

 ture of Space Internal Heat of the Earth Zone of Constant Temperature 



